0. Not sure if I understand your question but I have sent those SIMs as regular registered letters.
1. I have always used windowed envelopes in the
international standard "DL" format (110x220mm). The inserted A4-sized pages were addressed using Deutsche Post's online stamp service "Internetmarke" which produces address fields like this:
2. The letters contained just the MiniSIM (2FF) which I had always sticked to the very centre of the inserted page using small photo stickers.
3. I can't see any good reason why I should deserve heightened scrutiny and I would hardly make this public in the contrary case.
4. The letters were insured up to a maximum amount of 30 SDR (special drawing rights, 1 SDR ~ 1.50 USD) but I only received the actual value of the SIM cards plus shipping costs. Actually I have lost a few cents each time because PayPal's refund deadline had exceeded before I was refunded by Deutsche Post and so I had to send slightly more money than I received in order to cover the deducted PayPal fees.
5. Indeed it could just be the American sorting machines that have an issue with the European envelope format or the window position but I assume they would have found out long time ago as this is perhaps the most spread envelope format in Europe and there are probably ten or hundred thousands letters making it over the Pond daily.
Speaking of machines and humans, why do you start numbering with zero?
I'm not a supporter of conspiracy theories either but I wouldn't completely rule out such measures like confiscating suspicous SIM cards that originate from unclassifiable individuals, be it intentionally or by mistake. That's why I ask if anyone has made similar observations.